A photocoupler including a photorelay can convert an input electrical signal into an optical signal using a light emitting element, receive light using a light receiving element, and then output an electrical signal. Hence, the photocoupler can transmit an electrical signal in a state where the input side and the output side are insulated from each other.
In equipment such as industrial equipment, office equipment, and household electrical equipment, in many cases different power supply systems such as a DC voltage system, an AC power supply system, a telephone line system, and a control system are arranged in one device. However, if different power supply systems and circuit systems are directly connected, an operational malfunction may occur.
If the photocoupler is used, insulation is provided between different power sources and therefore the operational malfunction can be suppressed.
For example, a large number of photocouplers, including those for AC loads, are used in inverter air conditioners etc. In the case of being used for signal switching for LSI tester uses, a very large number of photocouplers are mounted. In such a case, downsizing is strongly required from the necessity to reduce the area of mounting onto a substrate.